1. Field of the Invention
The present invention relates to a semiconductor integrated circuit apparatus, and particularly to a semiconductor integrated circuit apparatus automatically restoring data stored to a plurality of logic circuits connected in series in an event of data loss due to noise or soft error.
2. Description of Related Art
In recent years, a manufacturing process of a semiconductor integrated circuit apparatus becomes more and more miniaturized. A semiconductor integrated circuit apparatus formed in such a miniaturized manufacturing process consumes low operating power supply voltage having small parasitic capacity in devices. Accordingly in such semiconductor integrated circuit, data stored in a logic circuit mounted therein may be lost due to noise or soft error.
The noise here indicates a noise generated due to an interference of adjacent lines in a semiconductor integrated circuit apparatus, an external noise supplied externally, or a noise generated at a junction of a synchronous circuit and an asynchronous circuit. These noises cause an amplitude of a signal waveform to be smaller, or rising edge of a signal may be delayed for example.
The soft error here indicates an error that in case radiation (for example neutron radiation and a radiation) is inserted to a semiconductor integrated circuit apparatus, a semiconductor substrate reacts with the radiation, generating a charge, and a logic is inverted by a plurality of the generated charges in output devices of a logic circuit being collected.
Such noise or soft error could disable a circuit to recognize a synchronizing clock that activates the circuit because the noise and soft error reduce an amplitude of a signal. Further, even with a reduction in the amplitude small enough for the circuit to still recognize the signal, the signal could delay while the signal transmits through lines due to parasitic resistance or capacity in the lines or devices. In this case also, the circuit is disabled to recognize the signal. In case an amplitude of a signal waveform is reduced due to the noise and soft error, a circuit may induce a malfunction, thereby losing data stored in a logic circuit, for example.
A loss of data is described hereinafter in detail. A circuit having a plurality of logic circuits connected in series is explained as an example. A circuit of shift register as an example of such circuit is shown in FIG. 6. A shift register 2 shown in FIG. 6 includes registers REG0 to REG7 connected in series. An output from the REG7 is connected to an input of the register REG0. A clock CLK is input to each of the registers REG0 to REG7. The shift register synchronizes with the clock CLK to operate. Outputs from the REG3 to REG5 are connected to blocks not shown, with control signals A to C to the blocks. The control signals A to C are signals used to control the blocks.
A timing chart of the shift register 2 of FIG. 6 is shown in FIG. 7. As shown in FIG. 7, at time t0 where power is turned on for the shift register, data 1 is set to the register REG0 by a power-on reset operation. At this time, data 0 is set to other registers. After the time t0, data 1 transits to a register connected subsequently in response to a rising edge of the clock CLK. At time t7, data 1 is stored to the register REG7 by this operation. Then data 1 is returned to the register REG0 at a rising edge of the clock at time t8. That is, the shift register 2 shown in FIG. 6 is a circuit that data 1 transits in a loop of the registers REG0 to REG7 in response to rising edges of clocks.
A timing chart in case data is lost in the shift register 2 operating as above is shown in FIG. 8. As shown in FIG. 8, in case an amplitude of a clock to be input at time t3 is reduced due to noise or soft error, the REG3 is not activated even with the REG2 being activated. Further, data 1 stored to the REG2 does not transit to the REG3 and is lost. The lost data is not restored until turning on the power again.
A specific example of the shift register is disclosed in Japanese Unexamined Patent Application Publication No. 2004-294224. The shift register disclosed in Japanese Unexamined Patent Application Publication No. 2004-294224 includes 5 registers connected in series, having an exclusive or of outputs from first, third, and fifth stages as an input of the first stage. This shift register generates patterns of random numbers. In case data 1 stored to a register is lost due to noise or soft error, this circuit also generates a pattern different from a correct pattern of random numbers. Further, all data stored to a register may become data 0 depending on a status of the pattern of random numbers. In such case, data 1 cannot be transited after that as with the shift register shown in FIG. 6.